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nsenter: fix up comments #1165

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Oct 31, 2016
Merged

nsenter: fix up comments #1165

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23 changes: 15 additions & 8 deletions libcontainer/nsenter/nsexec.c
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Original file line number Diff line number Diff line change
Expand Up @@ -447,10 +447,17 @@ void nsexec(void)
/*
* Okay, so this is quite annoying.
*
* In order to make sure that deal with older kernels (when CLONE_NEWUSER
* wasn't guaranteed to be done first if you specify multiple namespaces in
* a clone(2) invocation) as well as with certain usecases like rootless
* containers, we cannot just dump all of the cloneflags into clone(2).
* In order for this unsharing code to be more extensible we need to split
* up unshare(CLONE_NEWUSER) and clone() in various ways. The ideal case
* would be if we did clone(CLONE_NEWUSER) and the other namespaces
* separately, but because of SELinux issues we cannot really do that. But
* we cannot just dump the namespace flags into clone(...) because several
* usecases (such as rootless containers) require more granularity around
* the namespace setup. In addition, some older kernels had issues where
* CLONE_NEWUSER wasn't handled before other namespaces (but we cannot
* handle this while also dealing with SELinux so we choose SELinux support
* over broken kernel support).
*
* However, if we unshare(2) the user namespace *before* we clone(2), then
* all hell breaks loose.
*
Expand Down Expand Up @@ -623,9 +630,9 @@ void nsexec(void)
* containers). But for now, it's not possible to split this into
* CLONE_NEWUSER + [the rest] because of some RHEL SELinux issues.
*
* We also can't be sure if the current kernel supports
* clone(CLONE_PARENT | CLONE_NEWPID), so we'll just do it the long
* way anyway.
* Note that we don't merge this with clone() because there were
* some old kernel versions where clone(CLONE_PARENT | CLONE_NEWPID)
* was broken, so we'll just do it the long way anyway.
*/
if (unshare(config.cloneflags) < 0)
bail("failed to unshare namespaces");
Expand Down Expand Up @@ -701,7 +708,7 @@ void nsexec(void)
syncfd = syncpipe[0];

/* For debugging. */
prctl(PR_SET_NAME, (unsigned long) "runc:[1:INIT]", 0, 0, 0);
prctl(PR_SET_NAME, (unsigned long) "runc:[2:INIT]", 0, 0, 0);

if (setsid() < 0)
bail("setsid failed");
Expand Down